/*
 * Copyright 2000-2011 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.intellij.openapi.roots;

import com.intellij.openapi.components.ServiceManager;
import com.intellij.openapi.project.Project;
import com.intellij.openapi.util.ModificationTracker;

/**
 * @author yole
 */
public abstract class ProjectRootModificationTracker implements ModificationTracker {
  private static final ProjectRootModificationTracker NEVER_CHANGED = new ProjectRootModificationTracker() {
    @Override
    public long getModificationCount() {
      return 0;
    }
  };

  public static ProjectRootModificationTracker getInstance(Project project) {
    ProjectRootModificationTracker instance = ServiceManager.getService(project, ProjectRootModificationTracker.class);
    if (instance == null) return NEVER_CHANGED;
    return instance;
  }
}
